There are methods and burners for burning the black oils wherein the pulverization of the fuel is effected by means of steam or compressed air. Burners utilizing pulverization by means of low-pressure air at 250 kgf/m.sup.2 (kilogram-force per square meter) are used for black oils with up to 300 kg/h (kilograms per hour) average flow rate. These burners may be of the vortex type, the vortex motion being produced by means of the tangential introduction of the air into the burner housing or by guide blades.
The main disadvantage of pulverization by steam or compressed air is the high cost of the pulverization agent and the need for sources of steam or compressed air which often must be of large capacities.
There are also methods and burners in which the pulverization of the fuel is performed at high pressures with moderate and small flow rates requiring nozzles with a very small diameter.
The disadvantage of the latter systems is that small nozzles clog very easily and produce abnormal fine pulverization and flames.
Another burner with liquid fuel is known in which the pulverization is carried out in two stages at low pressure. In the first stage pulverization is performed by the air which enters through a plurality of apertures in a profiled body; this body may be axially moved thus decreasing, at lower levels of operation, the flow cross section through which the air passes for the second stage of pulverization.
This type of burner also has the disadvantage of an abnormal pulverization of the fuel and of nozzle clogging.